let (one) at (someone or something)
1. To allow one to have access to someone or something. Let me at the control panel, and I'll try to see what's causing the problem.
2. To allow one to attack someone or something. Let me at him, let me at him! I'll tear him limb from limb!
let someone or something at someone or something
to permit someone or something to attack or get at someone or something. He did that? Just let me at him! Let the committee at her, then she'll change her tune.